Method for introducing iodine into a lamp envelope



Nov. 13, 1962 E. G. AUDESSE METHOD FOR INTRODUCING IODINE INTO A LAMPENVELOPE Filed April 12, 1961 iim il l INVHVTOR.

MERY G. AUDESSE A TORNE United States Patent C) 3,063,778 METHOD FORINTRQDUCING IODINE INTO A LAMP ENVELOPE Emery G. Audesse, Salem, Massassignor to Sylvania Electric Products Inc, a corporation of DelawareFiled Apr. 12, 1961, Ser. No. 102,480 5 Claims. (Cl. 316-25) Thisinvention relates to lamps having tungsten filaments enclosed inenvelopes, the latter usually being of fused quartz or other suitableglass. Such devices are generally called iodine or iodine-quartz lamps.More particularly this invention concerns an improved method forintroducing controlled quantities of iodine into such lamps during themanufacturing process.

Incandescent lamps having quantities of iodine in the envelope are knownto the art. Such lamps operate on a tungsten-iodine cycle which is aregenerative, continuing process in which tungsten iodide is producedwhen the iodine combines chemically with particles of tungstenevaporating from an incandescing tungsten filament. Subsequent thermaldecomposition of this compound replaces the tungsten particles on thefilament. In conventional filament lamps not containing controlled quantities of iodine, these particles are deposited on the envelope, thusgradually causing a loss of light output due to blackening, Rupturing ofthe filament may occur when a sufiicient quantity of tungsten particlesevaporates and the lamp must be replaced. However, the iodine-tungstencycle eliminates lamp blackening and reduces lamp outage by its getteraction.

The iodine, together with the heat of the lamp, prevents the tungstenfrom accumulating on the lamp envelope and darkening it. As thevaporized tungsten iodide circulates back into the area of theincandescent filament, the intense heat of the filament frees thetungsten from the tungsten iodide by thermal decomposition and thistungsten is deposited back on the filament, leaving the iodine free tobegin a new cycle. Theoretically, if the evaporating tungsten particlescould be returned to the filament in a perfectly even coating, the lampmight never burn out. But since there is no way to control exactly wherethe tungsten particles return to the filament, one spot will eventuallywear out, thus rendering the iodine-quartz lamp inoperative. Thiscondition, however, occurs after operation in the order of hundreds ofhours and possibly even thousands of hours before lamp failure.Furthermore, during the life of an iodine lamp the maintenance of lightoutput is substantially constant.

The iodine present in the lamp envelope must be in controlled quantitiesand, in particular, must be in an adequate quantity to elfect aregenerative getter action, but inadequate to absorb appreciablequantities of light. Previous methods of adding the iodine to the lampenvelope to effect such regenerative getter action have been tedious andtime consuming and, furthermore, have tended to introduce undesirableimpurities into the lamp which shorten its life. Such methods have madeuse of a time-consuming operation of installing traps in the exhausttubing of the lamp; for example, a glass container with a supportingtungsten spring was slipped into the exhaust tubing to support theiodine crystals. These traps were previously necessary to position theiodine securely during an exhaust and fill step, but the disadvantagesof their use were the expense of fabrication together with thepossibility of vaporizing impurities from the trap into the lamp.

According to my process, materials not directly contribtuing to theaddition of iodine into the exhausted lamp are eliminated. My processcomprises placing iodine crystals of a random quantity intermediate theends of an exhaust tube that is appended to the side of the "ice 2 lampenvelope and the bore of which is in communication with the interior ofthe envelope.

The iodine crystals are then melted by gently warming the exhaust tubeover a gas flame, thus causing themelted iodine to wet the inside wallof the exhaust tubing. Upon cooling, the solidified iodine will adheretenaciously to the internal surface of the tube and will not bedisplaced even during the operations of exhausting and filling theenvelope. After such operations, the envelope is sealed from theatmosphere by fusing the glass of the exhaust tube at a point below theadhering iodine. 'Ihe sealed lamp is then placed in a constanttemperature bath for a sufficient time to vaporize controlled quantitiesof iodine from the exhaust tube to the envelope. After adequatequantities of iodine are vaporized, the lamp is removed from theconstant temperature bath, washed and chilled to reduce internal gaspressures. The exhaust tube is then sealed from the envelope at a pointclosely adjacent to the lamp envelope to produce the finished lamp.

Accordingly, an object of my invention is to prepareincandescent lampshaving controlled quantities of iodine in the envelope by an eificientand inexpensive process.

Another object of my invention is to introduce iodine into lampenvelopes in a manner so as to avoid con-- tamination and further, toproduce batches of lamps containing uniform quantities of iodine.

An advantage of my invention is that lamps containing uniform quantitiesof iodine may be produced without the introduction of undesirablecontaminating material, even though closely controlled quantities ofiodine are enclosed in each envelope.

A feautre of this invention is wetting the inner surface of an exhausttube with a random quantity of melted iodine and then allowing theiodine to solidify, thereby permitting the entrance and exit of gasesthrough the exhaust tube during lamp fabrication methods, withoutdislodging the iodine.

Other objects, features and advantages will become apparent to thoseskilled in the art upon reading the following specification when takenin conjunction with the accompanying drawings.

The various figures of the drawings are the schematic views in thenature of a flow. sheet depicting the various treatment steps in mymethod of inserting controlled quantities of iodine in the lampenvelope. For

simplicity, the tungsten filament is shown only in FIGS." 1 and 10,although it is to be understood that the filament is present in lampsshown in each and every treating step of FIGS. 2-9 respectively,

FIGURE 1 is an elevational view of a quartz-iodine lamp beforeevacuation and before insertion of the iodine.

FIGURE 2 is a schematic elevational view of a quartziodine lamp andshows in particular the insertion of a quantity of iodine crystals intothe exhaust tube with a FIGURE 3 is a schematic elevational view of thespatula. t, z

quartz-iodine lamp showing in particular the heating of the iodinecrystal to wet the walls of the tube.

FIGURE 4 of the drawing is a schematic elevational view of thequartz-iodine lamp being exhausted of atbath, which is shown in crosssection.

FIGURE 7 is a schematic elevational View of the quartz-iodine lamppositioned in a washing tank, which is shown in cross section.

FIGURE 8 is a schematic elevational view of the quartz-iodine lamppositioned in a tank of liquid nitrogen, which is shown in crosssection.

FIGURE 9 is a schematic elevational view illustrating the tippingoperation for the removal of the exhaust tube and sealing of the lamp.

FIGURE 10 is an elevational view of a completely fabricatedquartz-iodine lamp.

In each of the figures of the drawing similar numerical designations areindicative of similar elements of structures.

Referring to FIGURE 1 of the drawing, the lamp illustrated thereincomprises a high silica content glass envelope 1, preferably of fusedcrystalline quartz or possibly of fused vycor. The diameter of theenvelope may be, for example, to /2 inch, although other diameters arepossible. Each end of the envelope is flattened into a press or sealportion 2 and hermetically sealed and embedded therein are lead-inconductors which comprise outer sections 3 of molybdenum wire, innersections of tungsten wire and intermediate thin foil sections 4 ofmolybdenum. Each of the inner and outer sections, 3 and 5 respectively,is attached to the molybdenum foil section 4 by spot welding, solderingor merely puncturing, although other means for establishing electricalcontact may be used. A coiled coil filament 6 of tungsten wire extendsaxially of the envelope 1 and is connected at its ends to the inner endportion 5 of the lead-in conductors. Appended to the central portion ofthe glass envelope 1 is an exhaust tube 10, the bore of which is incommunication with the interior of the envelope 1.

In the first step of the operation, the assembly of the envelope 1 andexhaust tube It) is grasped by the exhaust tube 10 and horizontallyoriented. Care must be exercised in the handling of the envelope 1 sothat per piration and oils present on the hands are not transferred tothe envelope, since such substances would tend to adhere to the surfaceof the lamp and cause devitrification of the envelope upon illuminationof the lamp. Devitrification may be avoided by handling only the exhausttube 10 or by carefully manipulating the envelope 1 with gloved hands,although other preventative methods such as described in the co'pendingapplication of Leo Duval, Serial No. 38,601, filed June 17, 1960 arealso applicable.

'The iodine crystals are inserted in the horizontally oriented exhausttube 10, as shown in FIGURE 2, by inserting a spatula 11 which hasrandomly selected quantitles, for example .4 gm. of iodine crystals onthe end thereof. For convenience, the handle 12 of the spatula 11 has agreater diameter than the internal bore of the exhaust tube 10 anduniform positioning of the iodine crystals in the exhaust tube 10 isinsured by placing the spatula handle 12 directly against the end of theexhaust tube 10.

After placing the iodine crystals within the exhaust tube 10, thespatula 11 is withdrawn and the exhaust tube 1 heated directly beneaththe crystals 14, in a gas flame 15, as shown in FIGURE 3. Such heatingshould be quite rapid and of relatively short duration so as to raisethe crystals to their melting point, thereby causing them to wet thewalls of the exhaust tube 10. Generally, temperatures above about 114 C.can be used, but care must be exercised to avoid overheating the iodinesince temperaturesin excess of 183 C. would cause the iodine to boil offor possibly oxidize, which would of course be detrimental to lampfabrication methods. Subsequent cooling of the melted iodine will causethe melted iodine to adhere tenaciously to the walls of the exhaust tube10. As illustrated in each of FIGURES 2 and 3, the exhaust tube 10 ishorizontally oriented while the iodine is inserted and during the iodinemelting process because if the exhaust tube 19 was vertically oriented,the iodine crystals would tend to fall into the envelope 1, therebyincreasing the possibility that improper quantities of iodine might beadded.

As shown in FIGURE 4, the exhaust tube 10 is inserted in a schematicallyillustrated exhausting and filling chamber. In this step, atmosphericand other gases present in the lamp envelope are withdrawn from the lampthrough exhaust tube 16 and fill gases are forced into the lamp throughexhaust tube 10. In both the exhausting and filling steps the gases willpass over the melted iodine crystals which tenaciously adhere to theexhaust tube walls and are not dislodged even by such gaseous movement.Apart from the iodine in the lamp which will be described later,suitable filling gases include argon, krypton, xenon and mixturesthereof, at substantial pressures, for example argon at a pressure ofseveral hundred mils. mercury, preferably about 600 mils. Such gaseousfillng not only retards vaporization of the tungsten filament, butapparently causes a more uniform deposition of tungsten back upon thefilament. Of course, in addition to the iodine and the gases mentionedabove, other fill gase may be added at other gas pressures when desired,if such additional gases are not detrimental to the efficient operationof the lamp and do not adversely affect the regenerative cycle of thetungsten and iodine.

After exhausting the lamp and filling the envelope 1 with appropriategases, the exhaust tube It) is tipped and sealed below the adheringiodide 14 as shown in FIGURE 5 In this manner, the entire assembly ofthe lamp envelope 1 together with the exhaust tube 10 is sealed from theatmosphere while all of the fill gases and the iodine are presenttherein. Methods available for tipping the exhaust tube 10 are thoseconventionally used in the art and may be, for example, the typeillustrated in the drawing wherein a flame 17 contacts the exhaust tube10 and melts the glass. It generally is important to make the seal aconsiderable distance below the adhering iodine 14 (generally about oneinch) since extremes in temperature due to the proximity of meltingglass might cause vaporization of the iodine and the possible additionof undesirable quantities of iodine to the lamp envelope. After suchsealing operations, the lamp is grasped by the exhaust tube 10 andtransferred to the next step of the operation and the residual exhausttube of the first sealing stage removed from the exhausting equipment 16and discarded.

Since the iodine 14- now adheres to the walls of the exhaust tube 10,steps must be made to transfer an appropriate quantity to the lampenvelope 1. Such transfer is acomplished as shown in FIGURE 6 of thedrawing wherein the lamp is suspended on support rods 20 with theexhaust tube down and immersed in a constant temperature bath 19containing a suitable heat conducting liquid, for example Dowtherm.Conveniently, the heat conducting liquid may be heated by connectingelectrical resistance elements 23 to an appropriate power source,although other suitable heating means may also be used. The bath 19 ismaintained at a constant temperature by connecting a thermostat 20 and athermocouple 21 to the resistance elements 23. Although heating timesmay vary depending upon the amount of iodine to be vaporized into theenvelope 1 and heating temperatures may also be varied, depending uponsuch requirements, it has been found that heating times of 15 to 30minutes and preferably 20 to 30 minutes when the bath temperature isbetween and 115 C. and preferably between and C. vaporizes at the lowerlimit sufiicient iodine to assure the regenerative getter process, but athe upper limit does not exceed that quantity which would result in anyappreciable absorption of light by the iodine vapor in an illuminatedlamp. For successful operation of the lamp, it has been found that theenvelope should contain iodine in quantities of at least 0.1 micrornoleper cubic centimeter to 1.0 micromole per cubic centimeter of bulbvolume.

After vaporizing the desired amount of iodine from the exhaust tube It}to the lamp envelope 1, the assembly is washed by immersing it in a coldwater bath 22 as shown in FTGURE 7. To prevent residual and unvaporizediodine 14 from falling from the exhaust tube 1e into lamp envelope 1,the lamp is suspended between a pair of support rods 28 with the exhausttube beneath the envelope 1. After a few minutes in the wash bath 22,the oil from constant temperature bath 19 is Washed oit and the lamp isready for a chilling operation as shown in FIG- URE 8.

The chilling-operation is accomplished by immersing the assembly of theenvelope and the exhaust tube It in bath 24, which contains a largequantity of liquid nitrogen. The chilling reduces internal gas pressuresof the lamp for the final tipping operation. After an immersion of shortduration, generally about one minute, the lamp 1 together with theexhaust tube 10 is withdrawn from the liquid nitrogen and transferred toa final sealing operation. In this sealing operation of passing theexhaust tube 10 between a pair of flames 26 (shown in FIGURE 9) theexhaust tube 16 is removed from the envelope 1 while the glass is stillcold from the liquid nitrogen. This final tipping seals the envelope 1from the exhaust tube 10 at a point closely adjacent to the lampenvelope. Residual or excess iodine present in the exhaust tube 10 isremoved together with the exhaust tube in this step.

The finished lamp is shown in FIGURE 10. As shown, the lamp envelope 1has been scaled from the atmosphere and separated from the exhaust tubeand this separation has produced a pointed tipped end 27. All of theele= ments of the lamp described with reference to FIGURE 1 are present,except the exhaust tube. The required quantity of iodine has been added.

It is apparent that changes and modifications may be made within thespirit of the instant invention. It is my intent, however, to be limitedonly by the scope of the appended claims.

As my invention I claimi L The process for adding controlled quantitiesof iodine to a glass envelope having a tungsten filament supportedtherein and having an exhaust tube appended to the side thereof, thebore of which is in communication with the interior of said envelope,the steps which comprise: inserting a small quantity of iodine in thebore of said exhaust tube intermediate the ends thereof; melting saidiodine crystals by heating said exhaust tube, thereby causing the meltediodine to wet the Walls of said tube; cooling said exhaust tube, therebysolidifying the melted iodine; exhausting gases from said envelope andsaid tube and then adding a fill gas there to; sealing said exhaust tubeat a point below the adhering iodine; heating said envelope and saidexhaust tube for a period of time adequate to vaporize sufficient iodinefrom said exhaust tube into said envelope to effect a regenerativegetter action with the tungsten of the filament, but inadequate toabsorb appreciable quantities of light; chilling said envelope to reduceinternal gas pressures and sealing said exhaust tube from said envelopeat a point near said envelope.

2. The process for adding controlled quantities of iodine to a glassenvelope having a tungsten filament supported therein and having a glassexhaust tube appended to the side thereof, the bore of said tube beingin communication with the interior of said envelope, the steps whichcomprise: melting a small quantity of iodine crystals while saidcrystals are positioned within and intermediate the ends of said tube;cooling said melted crystals whereby said crystals solidify and adhereto the walls of said tube; exhausing said envelope and said exhaust tubeof gasses held therein and then filling said envelope and said exhausttube with a fill gas; sealing the end of said exhaust tube below theposition of the adhering iodine; heating said adhering iodine for asufficient time to vaporized said iodine from said exhaust tube intosaid enveloped in quantities adequate to effect the regenerative getteraction with said tungsten filament, but inadequate to absorb appreciablequantities of light during subsequent operation of said lamp and sealingsaid envelope from said exhaust tube at a point near said envelope.

3. The process for adding controlled quantities 'of iodine to a glassenvelope having a tungsten filament supported therein and having a glassexhaust tube appended to the side thereof, the bore of said tube beingin communication with the interior of said envelope, the steps whichcomprise: inserting a small quantity of iodine crystals in said exhausttube intermediate the ends thereof; heating said iodine crystals to atemperature slightly above the melting point, thereby causing the meltediodine to wet the walls of said tube; cooling the melted iodine therebycausing the iodine to adhere to the walls of said exhaust tube,exhausting gases present in said envelope and said exhaust tube throughsaid exhaust tube and adding a fill gas to said envelope through saidexhaust tube; sealing said exhaust tube from the atmosphere at a pointbelow said adhering iodine; immersing said envelope and tube in a heatedconstant temperature bath for a sufi'icient time to vaporize saidadhering iodine into said envelope from said exhaust tube in quantitiesadequate to effect a regenerative getter action with said tungstenfilament, but inadequate to absorb appreciable quantities of lightduring subsequent operation of the lamp and sealing said envelope fromsaid exhaust tube at a point near said envelope.

4. The process for adding controlled quantities of iodine to a glassenvelope having a tungsten filament supported therein and having a glassexhaust tube appended to the side thereof, the bore of said tube beingin communication with the interior of said envelope, the steps whichcomprise: melting a small quantity of iodine crystals while saidcrystals are positioned in said tube intermediate the ends thereof;cooling said melted crystals, thereby causing said iodine to solidifyand adhere to the walls of said tube; exhausting gases present in saidenvelope and said exhaust tube through said exhaust tube and then addinga fill gas to said envelope through said exhaust tube; sealing saidexhaust tube from the atmosphere at a point below said adhering iodine;vaporizing said adhering iodine crystals from said exhaust tube intosaid envelope in quantities adequate to effect a regenerative getteraction with said tungsten filament, but inadequate to absorb appreciablequantities of light during subsequent operation and sealing saidenvelope from said exhaust tube at a point near said envelope.

5. The process for adding controlled quantities of iodine to a glassenvelope having a tungsten filament supported therein and having a glassexhaust tube appended to the side thereof, the bore of said tube beingin communication with the interior of said envelope, the steps whichcomprise: melting a small quantity of iodine crystals while saidcrystals are positioned in said tube intermediate the ends thereof;cooling said melted crystals thereby solidifying said crystals andcausing them to adhere to the walls of said tube, exhausting saidenvelope and said exhaust tube of gasses held therein and then fillingsaid envelope and said exhaust tube with a fill gas; sealing the end ofsaid exhaust tube at a point below the position of the adhering iodine;heating said adhering iodine for a sufficient time to vaporize saidiodine from said exhaust tube to said envelope and in sutficientquantities to effect a regenerative getter action with said tungstenfilament, but inadequate quantities to absorb appreciable quantities oflight, chilling said envelope and said exhaust tube, thereby reducinginternal gas pressures and sealing said envelope from said exhaust tubeat a point near said envelope.

References Cited in the file of this patent UNITED STATES PATENTS395,9'62 Edison Ian. 8, 1889

1. THE PROCESS FOR ADDING CONTROLLED QUAMTIES OF IODINE TO A GLASSENVELOPE HAVING A TUNGSTEN FILAMENT SUPPORTED THEREIN AND HAVING ANEXHAUSTED TUBE APPENDED TO THE SIDE THEREOF, THE BORE OF WHICH IS INCOMMUNICATION WITH THE INTERIOR OF SAID ENVELOPE THE STEPS WHICHCOMPRISES: INSERTING A SMALL QUANTITY OF IODINE IN THE BORE OF SAIDEXHUST TUBE INTERNEDIATE THE ENDS THEREOF; MELTING SAID IODINE CRYSTALSBY HEATING SAID EXHUSTED TUBE, THEREBY CAUSING THE MELTED IODINE TO WETTHE WALLS OF SAID TUBE; COOLING SAID EXHUSTE TUBE, THEREBY SOLIDIFYINGTHE MELTED IODINE; EXHAUSTING GASES FROM SAID ENVELOPE AND SAID TUBE ANDTHEN ADDING A FILL GAS FROM SAID ENVELOPE AND SAID EXHAUST TUBE AT APOINT BELOW THE ADHERING IODINE; HEATING SAID ENVELOPE AND SAID EXHAUSTTUBE FOR A PERIOD OF TIME ADEQUATE TO VAPORIZE SUFFICIENT IODINE FROMSAID EXHAUST TUBE INTO SAID ENVELOPE TO EFFECT A REGENATIVE GETTERACTION WITH THE TUNGSTEN OF THE FILAMENT, BUT INADEQUATE TO ABSORBAPPRECIABLE QUANTITIES OF LIGHT; CHILLING SAID ENVELOPE TO REDUCEINTERNAL GAS PRESSURE AND SEALING SAID EXHAUST TUBE FROM SAID ENVELOPEAT A POINT NEAR SAID ENVELOPE.